Approximately 100 billion thin-walled metal beverage cans are sold annually in the United States alone. Nearly all of these beverage cans have a stay-on-tab type closure according to my U.S. Pat. Nos. 3,967,752 and 3,967,753, which issued on Jul. 6, 1976. These closures are part of a can end or lid which is double seamed to the can body in a conventional manner with conventional equipment in a beverage filling line.
The stay-on-tab end has a number of attributes which have enabled it to remain the industry standard for over 20 years. These attributes include (a) the ability to be manufactured by commercially available machines; (b) low material and manufacturing costs; (c) low rates of defective ends produced by the end manufacturing lines; (d) nestability for ease and economy in handling the shells (blanks) and ends in the manufacturing lines, shipping them, and handling them in the beverage filling lines; (e) ease and speed of filling the can with the beverage and then seaming the end onto the can, again at low cost; (f) reliable containment and protection of the beverage during shipping, distribution, display, and handling and use by the consumer, with respect to carbonated as well as non-carbonated contents; (g) ease of opening by consumers of widely varying finger sizes, strengths, and dexterity; (h) consumer safety; (i) reliability of opening by consumers; (j) pourability; (k) drinkability; and (l) recyclability, in terms of both the value of its constituent material and the cost of recovering it.
The attribute most lacking in stay-on-tab ends is resealability.
Numerous attempts have been made to provide resealable threaded closures for beverage cans. Some of these merely sought to replicate, in the metal can and end, the structure of the neck and closure of a bottle neck and cap. Others employed more ingenious, and sometimes complex, solutions. Examples of such solutions and concepts used for other containers may be found in Henderson U.S. Pat. No. 2,771,218, Meissner U.S. Pat. No. 3,339,812, Salamone U.S. Pat. No. 3,401,819, Dubreul U.S. Pat. No. 5,292,025, and French patent 1,048,219.
Such solutions, including the simple as well as the complex, have not been commercially successful for at least two reasons. First, they have failed to match one or more of the attributes of the stay-on-tab closures listed above. Low cost is probably the criterion which is most frequently not satisfied. It is safe to say that if cost were no object, all of the remaining criteria could be satisfied. Second, these solutions have failed to equal or surpass conventional PET bottles and caps, which, though not possessing all the attributes of a can with a stay-on-tab closure, possess many of them and nevertheless have resulted in an excellent package for beverages.